1. Field of the Invention
The present invention relates to power source control in an image display device, an image display system and an electronic device each equipped with a plurality of control units.
2. Description of Related Art
The document 1 (Japanese Patent Application Laid-Open No. 2002-218343) discloses a configuration in which a single CPU sends a command to a power source control device to control a power supply state (e.g. on/off) of a power source as an example of power source control in a TV receiver.
Moreover, the document 2 (Japanese Patent Application Laid-Open No. H10-207742) discloses information processing equipment installing a power source controlling processor therein for controlling a main power source for a main processor.
The latest electronic device is often constituted as an integrated system composed of a plurality of control units. For example, an image display device is provided with a plurality of control units such as a panel driving unit supplying a driving signal to a display panel and an image processing unit outputting an image signal to the panel driving unit. Each control unit has a memory, which stores programs, and a CPU, and builds a peculiar control system. In such an electronic device, it is general that a single CPU bearing power source control receives a status signal from each control unit, and that the CPU controls a power source in order to realize a preferable operation as the whole system.
It is necessary to design a power source controlling CPU and its program in accordance with the specifications of the state signals of all of the control units. Consequently, when not all of the specifications are determined, the program of the power source controlling CPU cannot be completed, and it was difficult to create an effective program. Moreover, there is a problem that, when an alteration of the specifications pertaining to the sequence of turning on and off the power source occurred in another control unit, the program of the power source controlling CPU should be also altered and consequently the productivity of producing the program is bad.
On the other hand, recently, an electronic device building a volatile memory of a large capacity therein has also appeared. In such a device, a sequence of turning on and off a power source for stopping the power source after saving data stored in the volatile memory in a nonvolatile memory is sometimes requested. In such a sequence, because a waiting time until the turning off of the power source varies according to the data amount to be written in the nonvolatile memory, the complexity of power source control increases. Moreover, although it is necessary to take a safe margin into account for the waiting time, the larger the margin is set to be, the lower the response to the request of turning on or off the power source falls. Consequently, there is also a problem of causing a deterioration of operationality.